The subject invention relates to microclimate cooling, and a miniature cooling system that can be used for any purpose that requires a compact cooling system. Such applications include, but are not limited to, microelectronics cooling such as computer processors and laser diodes, personal cooling systems, and portable cooling systems.
Clothing that protects soldiers, first responders, and other emergency personnel from chemical, biological, nuclear, and/or other similar threats can subject the individuals to heat stress. Certain hazardous environments can require the use of PPE (personal protective ensembles) with level A protection, which can place the working individual in an encapsulating micro-environment. These PPE can significantly diminish the ability of the body to reject heat to the external environment, leading to symptoms ranging from muscular weakness, dizziness and physical discomfort to more severe, life-threatening conditions such as heat exhaustion or heat stroke. In any case, the operational performance of the personnel wearing PPE can become severely impaired. The use of an auxiliary, portable microclimate cooling system can mitigate these effects, eliminate heat stress casualties, and reduce water consumption. At the present time, the efforts to develop a microclimate system have been limited to existing design concepts and use of a large number of commercial off-the-shelf components. The subject microclimate system can incorporate miniaturization and MEMS technology, in order to provide performance that cannot be matched simply by using smaller versions of currently available designs.
An effective compact cooling system (Holtzapple and Allen, 1983) should preferably satisfy the dual requirements of a high coefficient of performance and a light and compact design. One example of an effective and useful microclimate system preferably would be able to remove at least 120 W of heat while consuming no more than 50 W of electrical power for at least about 4 hours of operation. This would suggest that for this particular example the microclimate system would have a coefficient of performance, or heat removal to power input ratio, of 2.4. In conventional designs, the requirements of a high coefficient of performance and a light and compact design typically work against each other.
Current cooling methods, such as thermo-electric cooling and traditional refrigeration cycles, have a high coefficient of performance and efficient design size within certain cooling ranges. While thermo-electric coolers have a coefficient of performance close to 1.0 and a very small volumetric design relative to the cooling capacity when operating in the 10 to 100 watt range, the coefficient of performance of commercially available thermo-electric devices tend be at or below 0.6 when applied to higher cooling capacities. In personal or portable cooling units heat removal rates of this range are inadequate. An alternative to mitigating the lack of performance and increase cooling capacity would be to use more units in series or parallel, thus increasing the overall size and weight of the cooling unit to beyond the limits of portable, microclimate dimensions.
Commercially available refrigeration cycles also have difficulties in satisfying the heat load requirements of microclimate and portable systems while maintaining a light and compact design. Commercially available unit designs are typically optimized for operation above a minimum cooling load of 500 watts, which is too much or unnecessary for microclimate systems. At or above this minimum cooling load refrigeration cycles exhibit a high coefficient of performance of almost never less than two and increases significantly with increasing heat load designs. Furthermore, the size and weight relative to the cooling capacity also decrease with increasing heat load designs. Application of these units to microclimate systems however is difficult due to the large size and weight of such units when scaling down to lower cooling ranges that are suitable for microclimate systems. It is extremely difficult to find a commercially available compressor alone which is smaller than 1 liter and weighs less than several pounds, and which is rated for a cooling load near or below 500 watts. The cycle would then need additional components such a condenser and evaporator to become effective.
Accordingly, there is need for a cooling system having a high coefficient of performance and a light compact design.